This invention relates generally to concrete finishing devices that provide smooth, continuous concrete surfaces of a substantially uniform grade and finish. More particularly, our invention relates to laser controlled grade fixing devices for concrete finishing of the type classified in U.S. Class 404, subclasses 84, 114, 118 and/or 120.
As recognized by those skilled in the concrete finishing arts, after concrete is initially placed during construction, the upper surface must be appropriately finished to give it a smooth, homogeneous and correctly textured surface and appearance. A wide variety of finishing devices, including screeds, have long been in use throughout the industry for treating plastic concrete. Known prior art systems include "bull" floats, various forms of finishing boards, strike-offs, pans, plows, blades and the like. Bull floats essentially comprise a flat wooden board attached to a handle, much like a broom handle. These floats are intended to be manipulated by a single worker. Strike-offs contact rough, unfinished plastic concrete with a rigid leading edge to initially form and grade fresh concrete.
It is well known that vibration facilitates concrete finishing, and many vibrating systems have previously been proposed. Vibration during screeding helps to settle the concrete and eliminate air voids. Also, it helps to densify and compact the concrete during finishing. Vibrational screeding also draws out excess water thereby increasing the cured strength of the placed concrete. A fine layer of component cement and sand aggregate are raised to the surface by vibration along with the excess water. This slurry aids subsequent fine finishing. In general, vibration promotes the attainment of a uniform product. Often screeds extend between and rest upon the forms between which the plastic concrete is actually confined. Forms constrain the concrete until it is set, and provide a working support for the typical screed or finishing machine.
The selection of blade design for a particular machine is based upon a variety of factors, such as the characteristics of the concrete being laid. Variables relating to concrete finishing result from the selected type and percent of aggregate, sand, cement, epoxy, ad-mix, and water. Temperature, slab thickness, slump and placement method also vary the application procedure. Those skilled in the art will recognize that the selected finishing equipment must be appropriately mated to the job demands. Thus in screeding, for example, an optimum blade must be chosen based on the condition of the concrete. If high slump concrete is to be screeded, a floating pan would be ideal. For finishing drier concrete, a heavier twin-bladed screed might be more desirable. In all cases it is desirable to provide a means that automatically insures level finishing. While laser equipped screeding systems are known in the art, the expensive laser and hardware control system associated with such screeds is not easily adaptable for use with other common finishing mechanisms.
J. Dewayne Allen, one of the present co-inventors holds several patents in the art of concrete placement and finishing. One such is a prior art self-propelled "triangular truss" screed that rides upon the aforementioned forms, namely U.S. Pat. No. 4,349,328. Additionally, U.S. Pat. No. 4,798,494 discloses a floating vibratory screed intended to facilitate the finishing of concrete with or without forms. Finally, Allen prior U.S. Pat. Nos. 4,316,715; 4,363,618 and 4,375,351 and the various references cited and discussed therein are germane to the general technology discussed herein. All the above patents have been assigned to the same assignee as the present case.
U.S. Pat. Nos. 4,650,366 and 3,386,901 disclose screeds capable of formless, self-supporting or floating operation. The latter patent speaks to a relatively heavy triangular truss screed adapted to be operated by two workmen without the use of forms. U.S. Pat. No. 4,650,366 discloses a light weight, portable vibrating screed including a central, extruded beam element. A floating screed manufactured by Les Placements Paro of Canada, although it is not necessarily prior art and is apparently unpatented, is believed relevant. It includes a floating pan that is physically offset from, and adjustably coupled to, a parallel and spaced-apart strike-off knife assembly.
U.S. Pat. No. 3,431,336 discloses a vibrating finishing screed adapted for use upon plastic concrete that apparently is capable of floating. U.S. Pat. No. 2,314,985 discloses a vibratory hand screed including a central, vibrated pan that is apparently adapted for use upon plastic concrete without support upon confining forms.
Another prior art floating screed of general relevance is disclosed in a video tape produced by the American Concrete Institute and The Portland Cement Association, entitled "Finishing Concrete Flatwork," that bears a Copyright date of 1984. Other prior art screeds, generally of the "form-riding" type, include those screeds disclosed in U.S. Pat. Nos. 4,340,351; 4,105,355; 2,651,980; 2,542,979; 3,095,789; 2,693,136; and 4,030,873.
Lasers are commonplace on the modern construction site. They are employed in surveying and general leveling operations. Fukukawa U.S. Pat. Nos. 4,861,189 and 4,854,769 disclose a system for paving inclined and/or curved surfaces. This system employs anchor vehicles and paving vehicles. The paving vehicles are secured to the anchor vehicles by wires. The connections of the wires to the anchor vehicles are controlled by means of a laser sensing device. Microcomputers control the shape of the paving devices to create compound and complex curves in paved surfaces. Two devices employing a vehicle with a boom terminating in a screed are disclosed in Hansen U.S. Pat. No. 5,039,249 and Quenzi U.S. Pat. No. 4,930,935. Each of these patents relates to an anchor vehicle and a telescoping boom extending horizontally from the vehicle. The boom terminates in a screeding device that may also employ augers and vibrators. A second Quenzi U.S. Pat. No. 4,978,246 discloses an apparatus and method for controlling laser guided machines. This patent relates to an improvement to the above Quenzi patent.
Most relevant to the present invention is Owens U.S. Pat. No. 4,752,156. It discloses a manually operated laser guided portable screed. This invention is basically a screed with a pair of laser sensors mounted to it. Operators manually adjust the height of the screed as they draw it across placed concrete in response to a signal from the laser sensor. All of the above mentioned devices use a stationary laser beacon which projects a plan of laser light in a 360 degree plane.
However, none of the prior art devices known to us provides a satisfactorily efficient system for controlling the finished elevation of a concrete surface without the use of forms or heavy machinery. No prior art device provides for finishing plastic concrete to a uniform elevation or at a uniform angle of grade employing conventional portable, formless, floating screeds. Such screeds can be conveniently and concurrently used for vibrating, striking-off, and float finishing. Particularly, no device disclosed by the prior art is suitable for use within a building or in other confined areas. Additionally, prior art devices are restricted to a designed use and are not adaptable to a variety of uses. The prior art devices cannot be combined to work in a gang configuration. Neither can the prior art devices be reduced to a limited number of components to facilitate use in tight spaces or to increase the efficiency of available resources. In the conventional, combination, floating, vibratory screed, the relationship between the buoyancy of the pan, the plastic concrete's resultant surface tension, and the overall center of gravity of the apparatus are harmoniously balanced. The prior art devices also fail to take advantage of these balanced characteristics.